Mobile vacuum sweepers and/or collection systems and the like have proven to be useful in a number of applications. Some uses of these devices typically include the use of a vacuum to pick up particulate matter and fluids. For example, truck-mounted vacuum cleaning systems have long been used to clean a wide variety of debris from areas such as waste collection areas of power plants, steel mills, and other industrial sites. Also, these types of vehicle-based systems are employed in non-industrial applications to remove debris of all kinds from streets and other locations. In some industrial applications, these systems enable efficient acquisition and moving of particulate matter and in a safe, relatively dust-free manner. In other applications, the removal of debris and the cleaning of streets and other sites yield environmental, safety as well as aesthetic benefits.
Typically, vacuum debris cleaning systems have a vacuum system to lift the debris or matter and one or more collection chambers into which the collected debris and other particulate material and/or fluids are deposited (such debris collection tanks or hoppers are commonly referred to as “debris bodies” in the art). A high velocity blower or fan generates a negative pressure, causing a stream of air to flow through a vacuum pick-up head and flexible hose or similar conveyance that induces the debris to flow from the collection site through a hose or a similar device, preferably a flexible hose, to the debris body in which heavier debris particles are deposited. The debris body may include a tortuous air path to allow debris to fall out of the air stream. However, lighter debris particles may tend to remain in the air stream and continue to move toward the blower and the exhaust where the dust may be released to the environment as part of the exhaust air from the air stream. Of course, exhausting fine particulate matter as a result of the incomplete capture of dust and debris is not acceptable. For various reasons, this type of material is desired to be captured and in fact, there are existing clean air and related laws which specify the operational parameters required to be met by operation of sweeping and vacuuming cleaning mobile vehicles and the like. For example, see SCAQMD rule 1186, concerning the control of air emissions from street sweepers.
In response to the desire to capture fine particulate matter, such as dust, in such operations, filter bags or sock filters are commonly employed to capture such fugitive airborne debris in vacuum cleaning systems. While generally effective at removing debris particles from the air stream, filter bags and sock filters can become clogged quickly and, accordingly, must be cleaned and/or replaced frequently, when brought into contact with many types of airborne debris particles.
As an adaptation to improve the performance of bag and sock filtration systems, purge systems that agitate or shake the filters or periodically deliver a charge of compressed air to the filters have been proposed (see, e.g., U.S. Pat. Nos. 4,336,040 and 5,409,512). Unfortunately, in practice most shaker and agitator systems have been shown to make only modest improvements in filter life. Moreover, such systems may require a large number of mechanical and/or pneumatic components and thereby increase the cost of the system as well as the likelihood of system failure. So, it can be seen that these adaptations, while effective, tend to add complexity and cost to the system and maintenance of the system.
Another approach to improving the capture of airborne debris particles is to use a tangential cyclone to separate heavier airborne debris particles before the air stream contacts the filter bags. Examples of such systems are described in European Patent Application 0 434 007 and U.S. Pat. No. 5,996,171. Such systems are further exemplified by Guzzler® and Ace®, which are vacuum trucks sold by the Federal Signal Corporation. While effective in many respects, the effective filter life and efficiency in such serial cyclone separator/bag-house filter systems still often remains shorter than the period of desired operation. Tangential cyclones tend to be bulky devices, necessitating a relatively large amount of space to accommodate them.
Another solution to the problem of removing detritus in a vacuuming operation is the use of a tortuous path as part of the capture process. Use of a tortuous path in a debris collection hopper permits particulate matter to drop out of the air stream. In this method, detritus or particulate matter and/or fluids is picked up with a vacuum head and conveyed through a container by way of a tortuous air path. The tortuous air path permits heavier solid and/or liquid particles to fall out of the air stream and are thus retained in the container. Use of this technique alone does not address fine airborne dust.
Another solution to the problem of removing dust involves the use of water to suppress dust. While effective, using a water spray or mixing system necessarily requires the carrying of a sufficient amount of water onboard. Naturally, this increases the weight and complexity of the vehicle and may impose limits as to its operation.
For these and other reasons, there remains a need for improved and alternative devices and systems for handling airborne debris in debris collection and particulate acquisition systems. The invention satisfies the need by providing such devices and systems, debris collection vehicles that incorporate such devices and systems, and methods of using such devices, systems, and vehicles. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.